Manufacture of slates

ABSTRACT

A slate-chamfering machine is disclosed which comprises at least one rotatably drivable cutting tool, the machine being adapted to present at least one edge of a substantially rectangular slate to the cutting tool, and feeding means for effecting relative movement between the cutting tool and the slate in a direction substantially parallel to the axis of rotation of the tool when the slate is presented to the tool, whereby the whole length of said edge may be roughly chamfered to achieve a &#39;&#39;&#39;&#39;naturally broken&#39;&#39;&#39;&#39; finish.

United States Patent [56] References Cited UNITED STATES PATENTS 2,958,163 11/1960 Cammerzell 125/26X 1,424,719 8/1922 Funk 125/26 2,731,961 1/1956 Ponseele 125/23 1,841,018 1/1932 Eickhoff..... 125/23 3,067,731 12/1962 Potter 125/3 FOREIGN PATENTS 76,830 5/1950 Norway 125/23 79,223 1950 Czechoslovakia 125/3 Primary Examiner-Harold D. Whitehead Attorney-Scrivener, Parker, Scrivener and Clarke ABSTRACT: A slate-chamfering machine is disclosed which comprises at least one rotatably drivable cutting tool, the machine being adapted to present at least one edge of a substantially rectangular slate to the cutting tool, and feeding means for effecting relative movement between the cutting tool and the slate in a direction substantially parallel to the axis of rotation of the tool when the slate is presented to the tool, whereby the whole length of said edge may be roughly chamfered to achieve a naturally broken" finish.

fag

Mag

Patented May 25, 1971 6 Sheets-Sheet 1 Patented May 25, 1971 6 Sheets-Sheet 2 I) f 1 m 2 H. J: U I WNIIII/ .1, Rm 9 u Lr fi R Wi mN Itl fin e m R In R k \L WQE Patented May 25, 1971 I 3,580,235

6 Sheets-Sheet 3 SI is \L Q A .I g I k I I I I I I a I mk I w I m I I I "W I I i I I I I I Patented May 25, 1971 6 Sheets-Sheet 4.

L L4 l YX///////////////J3 Patented May 25, 1971 3,580,235

6 Sheets-Sheet 5 MANUFACTURE or SLATES SUMMARY OF THE INVENTION Slate is a naturally occurring, fissile, fine-grained argillaceous rock which may be readily cleaved or split into thin I slabs having great tensile strength, durability and resistance to weathering. These slabs, or slates, are widely used for roofing purposes.

The present invention relates to the manufacture of roofing slates and in particular to a machine for chamfering the edges of slates.

Slate is a naturally occurring, fissile, fine-grained argillaceous rock which may be readily cleaved or split into thin slabs having great tensile strength, durability and resistance to weathering. These slabs, or slates, are widely used for roofing purposes.

ln the conventional manufacture of slates, a block of slate is sawn into a rectangular parallel-sided block by a steel or diamond saw. The block is then split along a plane of cleavage so as to form two thinner blocks. The blocks are further subdivided along planes of cleavage until the original block has been converted into a plurality of thin slabs.

The resulting square-edged slabs of slate are not generally acceptable as roofing slates. Before they will be found acceptable as a building material, it is necessary to chamfer the edges of the slate so as to give it a rough naturally broken" or rustic" finish. This finish to the slate edges provides a more aesthetically pleasing appearance to a roof constructed of the slates and also marginally improves the weatherproofing qualities of the roof by providing a sloping surface at the overlap of two slates for rainwater to run down.

Traditionally this chamfering operation has been performed by hand using a suitable handtool, such as a dressing knife or guillotine.

According to one aspect of the present invention a slate is chamfered by means of a rotatably driven tool.

According to a second aspect of the invention a slate-chamfering machine comprises at least one rotatably drivable cutting tool, the machine being adapted to present at least one edge of a substantially rectangular slate to the cutting tool, and feeding means for effecting relative movement between the cutting tool and the slate in a direction substantially parallel to the axis of rotation of the tool when the slate is presented to the tool, whereby the whole length of said edge may be roughly chamfered to achieve a naturally broken" finish.

Preferably the feeding means comprises at least one conveyor belt capable of moving the slate relative to the cutting tool in said aforementioned direction.

Preferably four cutting tools are provided along the length of the conveyor belt each tool being for chamfering one of the four sides of the slate respectively. A turning device is provided which is adapted to turn a slate through substantially 90. Each cutting tool has an associated pushover device for aligning a slate in a predetermined direction before it reaches that cutting tool, and an associated reference surface against which the pushover device is capable of urging the slate. Furthermore, each cutting tool is provided with means for maintaining the slates in alignment as they are chamfered by the cutting tool.

The cutting tool is conveniently a milling type cutter having a suitable number of cutting edges, for example a 6-inchdiameter milling cutter having two to 16 cutting edges.

The invention will be further described, by way of example, with reference to and as illustrated in the accompanying drawings, in which:

HO. 1 is a diagrammatic plan view of one embodiment of a slate-chamfering machine constructed according to the present invention illustrating the relative positions of its four chamfering stations.

FIG. 2 is a plan view of one of the chamfering stations of the machine of FIG. 1.

FIG. 3 is a front elevation through the line FF of FIG. 2.

FIG. 4 is a side elevation of one embodiment of a turning device for the machine of the present invention.

FIG. 5 is a diagrammatic side elevation of a cutting tool in contact with a slate.

HO. 6 is a sectional side elevation on the line RR of FIG. 2 showing the arrangement of the tracking rollers.

FIG. 7 is a diagrammatic plan view ofa second embodiment of a slate-chamfering machine constructed in accordance with the present invention.

FIG. 1 illustrates diagrammatically a chamfering machine in which a fiat parallel-edged conveyor belt 1 is arranged to carry substantially rectangular slates 2, having four sides 20, 2b, 2c and 24, past a series of four cutting tool stations 30, 3b, 3c, 3d and a turning station 7 located along the longitudinal axis of the conveyor belt I. The belt 1 is carried by a plurality of rollers, the end rollers 4 and 5 being illustrated in FIG. 1 and an intermediate roller 60 in FIG. 3. A motor and suitable reduction gear (not shown) are provided for driving the conveyor belt at a substantially constant speed, the normal belt movement being such as to convey slates in the direction of arrow K in FIG. 1.

Each chamfering station 3a, 3b, 3c, 3d has means for aligning a slate arriving on the belt at that station and a hydraulically driven cutting tool 60, 6b, 6c, 6d respectively.

Chamfering stations 3a and 3b are located on opposite sides of the conveyor belt 1 for chamfering opposite edges 20, 0, 2b of the slates respectively. Chamfering stations 3c and 3d are also located on opposite sides of the conveyor belt 1 for chamfering the remaining two edges 2c, 2d of the slates respectively, the turning device 7 turning the slates through approximately while they pass between chamfering stations 3b and 3c.

FIG. 2 shows the chamfering station 3a in more detail. The conveyor belt 1 moves in the direction of the arrow L. The cutting tool 6a is a milling type cutter having a plurality of teeth or cutting edges 11 (shown more clearly in H6. 5), the axis of rotation of the tool being substantially parallel to the direction of movement of the conveyor belt 1. The cutting tool 60 is mounted for rotation on a shaft 8, which is directly driven by a ZAhp. hydraulic motor 9 supported on a frame 10 of the machine, such that the longitudinal axis of the shaft 8 lies in the same plane as the top surface of a slate resting on the conveyor belt 1. The position of the motor 9, shaft 8 and cutter 6a may be adjusted in a direction substantially perpendicular to the edge 12 of the belt 1, the reason for which will be described below. The speed of the motor 9 may be adjusted by bypass valves (not shown) between the values of 1,500 to 4,800 rpm.

A pneumatically operated pushover device 13 is located on the frame 10 above the belt 1 such that a slate being conveyed by the belt 1 meets the pushover device 13 before it reaches the cutting tool 60.

The device 13 comprises a pneumatic cylinder 14 having a piston rod 15, to the free end of which is attached a crosshead 21. The extremities of the crosshead 21 have cylindrical bores 62 which slide on a pair of guide rods 18 firmly fixed to the frame 10. A second crosshead 16 is loosely carried on the piston rod 15 and is separated from the crosshead 21 by a cylindrical collar 22 and a coil spring assembly 23. Each extremity of the crosshead 16 is provided with a cylindrical collar member 17 which is slidably carried by one of the guide rods 18 respectively.

A portion of the crosshead 16 extends vertically downwards so that its bottom edge is parallel to, and just vertically spaced from the level of the top surface of the conveyor belt 1. A plurality of reference rollers 19 are located on the frame 10 so as to provide a surface which is parallel to said bottom edge of the crosshead l6 and also parallel to the longitudinal axis of the shaft 8.

Movement of the piston (not shown) within the cylinder 14 to the right as seen in FIG. 2, advances the crosshead 21 to the right in a direction substantially perpendicular to the direction of movement of the belt 11. This movement is transferred to the crosshead 16 via the collar 22 and spring assembly 23 which is thus also moved to the right.

If the movement of the crosshead 16 is stopped, the

crosshead 21 continues to move to the right compressing the spring assembly 23. A limit switch (not shown) is located on the pushover device such that when the crosshead 16 has been halted, after a predetermined movement to the right of the crosshead 21, the aforementioned switch is operated. This switch is arranged to control the supply of compressed air to the cylinder 14 such that operation of the switch initiates movement of the piston to the left. A proximity switch is located on the machine for controlling the supply of compressed air to the cylinder 14 so as to halt the piston when the crosshead 21 has reached the limit of its travel to the left and is in its inoperative position shown in FIG. 2.

The leading edge of a slate which is being transported by the belt 1 is arranged to operate a second proximity switch (not shown) which controls a solenoid air valve connected to the cylinder 14 of the pushover device 13 such that the crosshead 21 and consequently the crosshead 16 are caused to move to the right as seen in H6. 2. Each slate is fed onto the belt so as to lie with a pair of its opposite edges approximately parallel to the direction of movement of the belt 1. Thus as the crosshead 16 moves to the right, its bottom edge portion engages one edge of the slate and pushes the slated in the direction of the reference rollers 19. Eventually the slate is moved into a position in which it is in contact with both the crosshead 16 and the reference rollers 19. Further movement ofthe crosshead 16 to the right causes the slate to be reorientated until it is ac curately aligned with one pair of opposite edges parallel to the axis of the shaft 8. Movement of the crosshead 16 is now prevented by the slate but the crosshead 21 continues to move to the right until the limit switch is operated. The supply of air to the cylinder is then reversed so that the piston moves to the left returning both crossheads 16 and 21 to their left hand positions to await the arrival of the next slate.

Each chamfering station 3a, 3b, 3c and 3d has a pair of gantry members 25 (one shown in FIG. 3) each pair being adapted to support a set of four disc-shaped guide wheels 24. The four guide wheels 24 are mounted adjacent the four ends respectively of a pair of cylindrical rollers 61 which are journaled in respectively U-shaped frames 27. Each frame 27 carries a pair of screw-threaded bolts 28 which pass through bores in the gantry 25, the free ends of the bolts receiving nuts 29. A coil spring 38 is located around the shank of each of the bolts 28 to bias the frame 27 away from the gantry 2S. Loosely mounted supporting members 31 and 32 provide lateral support for the frames 27. Each pair of U-shaped frames 27 includes a crossmember 62, 63 respectively. The crossmember 62 has a pair of arms 64 loosely mounted thereon for angular displacement in planes perpendicular to the axis of the crossmember 62, a further disc-shaped guide wheel 65 being journaled between the free ends of the arms 64 on a pin 66. The crossmember 63 has a generally L-shaped member 67 loosely mounted thereon for angular displacement in planes perpendicular to the axis of the crossmember 63. The free end of the L-shaped member 67 is screw threaded and passes freely through an aperture in a block 68 which is loosely mounted between the arms 64 on pins 69. A coil spring 73, located around the free end of the L- shaped member 67, is constrained between the block 68 and a washer 7l'and nut 72, such that the downward pressure exerted by the guide wheel 65 may be varied by adjusting, the position of the nut 72.

The downward pressure exerted by the guide wheels 24 and 65 is sufiicient to ensure that a slate carried beneath the guide wheels 24 and 65 by the belt 1 aligned in a given position relative to the belt 1 will have that position maintained by the guide wheels 24 and 65 while the cutting tool operates on the slate.

Each of the other chamfering stations 3b, 3c and 3d is substantially identical in construction to the chamfering station which has been described in detail above, except that stations 3b and 3d are adapted to operate on the opposite side of the belt 1 from stations 3a and 3c.

The turning device 7 is located above the belt 1 between the chamfering stations 3b and 3c and comprises a suction cup 33 angularly displaceable relative to asupporting frame 70. The suction cup 33 is generally cylindrical having an open end 34 and a closed end 35, the closed end 35 having a cylindrical bore 36 whose longitudinal axis coincides with the longitudinal axis of the suction cup 33. A cylinder 37 having a closed end 38 is rigidly joined to the suction cup 33 such that its internal bore 39 forms a coaxial continuation of the bore 36 in the suction cup 33. A bore 40 (FIG. 4) in the cylinder 37 is adapted to receive a conduit (not shown) which is connected to a vacuum pump whereby the pressure in the suction cup 33 may be reduced.

The cylinder 37 has a collar 57 which is rotatably seated on a transverse member 41 having bores 42 therein (one shown in FIG. 4) slidably guided on pillars 43. The pillars 43 are rigidly mounted on an extension 44 of the frame 70 and are screw threaded to receive respective nuts 45 whereby to retain the transverse member 41. Each pillar 43 carries a coil spring 46 located between the frame extension 44 and the transverse member 41 whereby to bias the transverse member 41 in a direction away from said frame extension 44.

A ram, indicated generally in FIG. 4 by the reference numeral 47, is located on the frame 70 and is capable of imparting a downwardly directed force (arrow N in FIG. 4) to the cylinder 37 and suction cup 33. The ram 47 comprises a bifurcated supporting member 48 between the legs of which is pivoted at 55 a plunger 49 having a protuberance 50 on one end thereof, its other end 51 being connected to the piston of a compressed air ram (not shown). The closed end 38 of the cylinder 37 carries a screw-thread bolt 52 in a bore 53, the longitudinal axis of which is colinear with the longitudinal axis of the cylinder 37. A locknut 54 is provided for rigidly fixing the bolt 52 relative to the cylinder 37.

The supporting member 48 and the cylinder 37 are located relative to the frame 70 such that when the air ram is not actuated the protuberance 50 lies above and closelyspaced from the head of the bolt 52.

The cylinder 37 has a generally cylindrical collar 56 rigidly attached thereto. The collar 56 has an upstanding eccentrically mounted pin 58 which is adapted to receive a connecting rod linkage (not shown) operable by a second compressed air ram. Actuation of this second air ram is arranged to displace the connecting rod such that the collar 56 and hence the cylinder 37 and suction cup 33 are rotated through substantially The connecting rod linkage is constructed such that the above-described 90 turning action is substantially unaffected by the relatively small vertical displacements of the collar 56 initiated by the first mentioned air ram.

The air ram for depressing the suction cup 33 is actuated by a switch which is arranged to detect the leading edge of a slate which is approaching the turning device and which has just left the chamfering station 3b. Actuation of the ram causes the plunger to rotate about the pivot 55, the protuberance 50 encountering the bolt 52 and forcing the cylinder 37 and suction cup 33 to move downwards against the force of the coil springs 46.

it is arranged that when the suction cup 33 has reached its lowermost depressed position, the open end 34 thereof is firmly into sealing contact with that corner of the slate which is nearest to the leading edge in the direction of movement of the slate and also closely adjacent to the edge of the belt 1. When the suction cup 33 reaches this lowermost position a relay (not shown) is actuated which has a delay time of approximately 200 to 300 milliseconds. This delay allows the partial vacuum in the suction cup to drop to a value sufficient to support the weight of the slate. After the expiry of this delay the air ram depressing the suction cup 33 is deactuated by the relay and the suction cup 33 is raised by the springs 46 carrying the slate with it. Simultaneously the relay actuates the second air ram to effect rotation of the slate through substantially 90. A further switching mechanism (not shown) is arranged to cutoff the vacuum and effectively vent the suction cup when the 90 turning operation has been completed. The

slate is thus released and drops back onto the moving conveyor belt 1, the second air ram being deactuated to allow the suction cup 33 to rotate back through 90, under the action of a spring (not shown), to its original position.

With reference to FIG. 1, the turning mechanism is thus capable of turning a slate in the direction of the arrow 0 from the position shown in dotted lines at the turning station 7 to the position shown in solid lines. This operation should be repeatable at least once every second. The distance from the leading corner of the slate in contact with the reference rollers associated with the turning device to the center of the suction cup 33 is such that the turning circle produced does not lie in the way of any switch or working mechanism. 8

The chamfering machine described above operates in the following manner. A plurality of slates are fed one by one at short intervals onto the conveyor belt 1, two opposite edges being approximately parallel to the direction of movement of the belt (arrow K in FIG. 1). By way of example and where the slates are rectangular, HO. 1 shows the various stages through which a slate passes when it introduced to the belt 1 with its two longer edges approximately parallel to the direction K.

The leading edge of the first slate triggers the pushover device associated with chamfering station 30 as the slate approaches. The crosshead 16 is thereby caused to move towards the right-hand side (as seen in FIG. 2, and in the direction of arrow A in FIG. 1) of the belt 1 aligning the moving slate between itself and the reference rollers 19. The lead ing edge of the aligned slate is immediately carried under the first pair of guide wheels 24 which maintain the alignment while the crosshead 16 is returned to its inoperative position, that is, the position it occupies in FIG. 2. The edge 2a of the slate which had been in contact with the reference rollers 19 eventually reaches the cutting tool 6a in a position, substantially as illustrated in FIG. 5, such that the top surface of the slate lies in substantially the same plane as the longitudinal axis of the shaft 8 and a cutting edge, at the moment of impact with the slate, overlaps the slate by a small distance R. This overlap is conveniently approximately one-sixteenth to three thirty-seconds of an inch.

The slate 2 is moved progressively past the cutting tool until the whole of the edge 20 has been chamfered. The relative spacing of the chamfering stations 3a, 3b is such that as soon as the trailing edge 2c of the slate 2 leaves the second pair of guide wheels 24 the leading edge of the slate triggers the pushover device associated with the second chamfering station 3b. The crosshead of this pushover device moves the slate in the direction of arrow B (FIG. 1) so as to realign the slate against the corresponding reference rollers. The slate is carried under the associated guide wheels and past the cutting tool 6b so that the edge 21) is chamfered in the same manner as the opposite edge 2a.

The relative spacing of the chamfering station 3b and the turning station 7 is such that as soon as the trailing edge 2c of the slate 2 has left the second pair of guide wheels 24 of the station 3b, the first air ram is triggered to lower the suction cup 33. A turning cycle is then completed as described previously to realign the slate with the already chamfered edge 2a now leading.

The relative spacing of the turning station 7 and the chamfering station 3c is such that as soon as the trailing edge 2b has passed beneath the suction cup 33, the pushover device of the third chamfering station 3c is triggered and the corresponding crosshead advanced in the direction of the arrow C (FIG. 1) to align the slate 2 against the associated reference rollers. The slate is carried under the guide wheels and past the cutting tool 6c so that the edge 2c is chamfered in the same manner as the edges 2a, 2b.

The relative spacing of the chamfering stations 3c, 3d is such that as soon as the trailing edge 2b leaves the second pair of guide wheels 24 of the station 30, the pushover device of the fourth chamfering station 3d is triggered and the corresponding crosshead advanced in the direction of the arrow D (FIG. 1) to align the slate 2 against the associated reference rollers.

The slate is then carried under the guide wheels and past the cutting tool 6d so that the edge 2c is chamfered on the same manner as the edges 2a, 2b, 2c.

Slates thus arrive at the discharge end of the conveyor belt 1 having been chamfered along all four edges and may be transferred to discharge or loading station (not shown) by further conveyor belt means.

The adjustment of the position of the axis of the shaft 8 relative to the conveyor belt is provided for varying the degree and type of chamfering of the slates as desired. The width of the cutting tool is determined by the rate of chamfering and the appearance sought for the slate. The width of the tool is also related to the speed of rotation thereof.

The pushover devices are capable of aligning slates having a maximum length of between 7 and 20 inches.

FIG. 7 illustrated diagrammatically a second embodiment of a chamfering machine in which the 90 turning operation is accomplished by replacing the single conveyor belt 1 by a pair of conveyor belts 80, 81 which extend at right angles to each other. A substantially rectangular state 82, having four sides 82a, 82b, 82c and 82a, is carried by belt past a first cutting tool station 83a at which the slate edge 82a is chamfered. The cutting tool station 83 is identical to the cutting tool station 3a. A pushover device (not shown) is arranged to urge the slate 82 in the direction of the arrow H to align the slate prior to its passage past the cutting tool station 83a.

The slate is then moved in the direction of arrow G by the conveyor 80 towards a second cutting tool station 83b. A second pushover device (not shown) is arranged to urge the slate 82 in the direction of arrow E to align the slate prior to its passage past the cutting tool station 83b where the slate edge 82b is chamfered.

The conveyor carries the slate 82 in the direction of arrow G until it comes into the region of a further pushover device (not shown) which pushes the slate 82 in the direction of arrow P from conveyor 80 onto conveyor 81. The conveyor 81 carries the slate 82 in the direction of arrow 5 towards a third cutting tool station 83c. Prior to its arrival at this station 830, the slate is aligned by a pushover device (not shown) which acts in the direction of arrow T to present edge 820 to the tool station 83c.

The conveyor 81 then carries the slate towards a final cutting tool station 83d. Prior to its arrival at this station 83,the slate is aligned by a pushover device (not shown) which acts in the direction of arrow W to present edge 82d to the tool station 83d.

Apart from the means for turning the slate through the component parts of the machine illustrated with reference to FIG. 7 are substantially identical to those described in detail with reference to FIGS. 1 to 6.

We claim:

1. A slate-chamfering machine comprising:

a frame; feeding means on the frame for carrying one or more rectangular slates presented thereto along the length of the frame; four rotatably drivable cutting tools mounted at spaced locations on the frame, each tool being for chamfering one of the four sides of the rectangular slate respectively, and the shaft of each tool being arranged such that its longitudinal axis lies in the same plane as the upper surface of the slate carried by said feeding means; tooth means on each tool adapted to travel downwards at the line of contact with a slate presented to the tool when the tool is rotated; four fluid-operated pushover devices mounted on the frame adjacent respective ones of the cutting tools for aligning a slate in a predetermined direction before it reaches that cutting tool; a reference surface associated with each cutting tool against which the pushover device is capable of urging a slate for alignment thereof; means for maintaining the slates in alignment when they are chamfered by that cutting tool; and means for turning the slates individually through substantially 90 between the second and third ones of said cutting tools.

2. A machine according to claim 1 in which the feeding means comprises a single endless belt and the turning means is located on the frame intermediate the second and third cutting tools, the first and second cutting tools being located adjacent opposite edges of the belt and the third and fourth cutting tools also being located adjacent opposite edges of the belt.

3. A machine according to claim 2 in which the first and third cutting tools are located adjacent one edge of the belt and the second and fourth cutting tools and the turning device are located adjacent the other edge of the belt.

4. A machine according to claim 2 in which the turning means comprises a suction cup which is adapted for engaging attachment to a slate and which is capable of being angularly displaced by substantially 90 to change the angular disposition of the slate relative to the feeding means.

5. A machine according to claim 1 in which the feeding means comprises two endless belts, arranged at right angles to one another on said frame in a generally L-shaped configuration to provide said turning means, first and second cutting tools being mounted on said frame adjacent opposite edges of one of said belts and third and fourth cutting tools being mounted on said frame adjacent opposite edges of the other of said belts.

6. A machine according to claim 1 in which each pushover device comprises a pneumatically operable cylinder mounted above a respective conveyor belt having a piston connected to a crosshead, the crosshead being adapted to move from an inoperative position into engagement with a slate carried under the pushover device on the respective conveyor belt whereby to urge the slate towards the associated reference surface.

7. A machine according to claim 1 in which the means for maintaining the slates in alignment comprises two tracking rollers, each carrying a guide wheel adjacent both ends thereof for guiding the slates, and a third tracking roller carry ing a guide wheel and located with its axis intermediate the axes of the first-mentioned tracking rollers, the axes of all three rollers being substantially parallel to each other and substantially perpendicular to the axis of rotation of the cutting tool. 

1. A slate-chamfering machine comprising: a frame; feeding means on the frame for carrying one or more rectangular slates presented thereto along the length of the frame; four rotatably drivable cutting tools mounted at spaced locations on the frame, each tool being for chamfering one of the four sides of the rectangular slate respectively, and the shaft of each tool being arranged such that its longitudinal axis lies in the same plane as the upper surface of the slate carried by said feeding means; tooth means on each tool adapted to travel downwards at the line of contact with a slate presented to the tool when the tool is rotated; four fluid-operated pushover devices mounted on the frame adjacent respective ones of the cutting tools for aligning a slate in a predetermined direction before it reaches that cutting tool; a reference surface associated with each cutting tool against which the pushover device is capable of urging a slate for alignment thereof; means for maintaining the slates in alignment when they are chamfered by that cutting tool; and means for turning the slates individually through substantially 90* between the second and third ones of said cutting tools.
 2. A machine according to claim 1 in which the feeding means comprises a single endless belt and the turning means is located on the frame intermediate the second and third cutting tools, the first and second cutting tools being located adjacent opposite edges of the belt and the third and fourth cutting tools also being located adjacent opposite edges of the belt.
 3. A machine according to claim 2 in which the first and third cutting tools are located adjacent one edge of the belt and the second and fourth cutting tools and the turning device are located adjacent the other edge of the belt.
 4. A machine according to claim 2 in which the turning means comprises a suction cup which is adapted for engaging attachment to a slate and which is capable of being angularly displaced by substantially 90* to change the angular disposition of the slate relative to the feeding means.
 5. A machine according to claim 1 in which the feeding means comprises two endless belts, arranged at right angles to one another on said frame in a generally L-shaped configuration to provide said turning means, first and second cutting tools being mounted on said frame adjacent opposite edges of one of said belts and third and fourth cutting tools being mounted on said frame adjacent opposite edges of the other of said belts.
 6. A machine according to claim 1 in which each pushover device comprises a pneumatically operable cylinder mounted above a respective conveyor belt having a piston connected to a crosshead, the crosshead being adapted to move from an inoperative position into engagement with a slate carried under the pushover device on the respective conveyor belt whereby to urge the slate towards the associated reference surface.
 7. A machine according to claim 1 in which the means for maintaining the slates in alignment comprises two tracking rollers, each carrying a guide wheel adjacent both ends thereof for guiding the slates, and a third tracking roller carrying a guide wheel and located with its axis intermediate the axes of the first-mentioned tracking rollers, the axes of all three rollers being substantially parallel to each other and substantially perpendicular to the axis of rotation of the cutting tool. 